Peristaltic pump

ABSTRACT

A peristaltic pump, which provides a relatively rigid tubular body (2); a contained substantially tubular elastic element (1), with an outside diameter less than the inside diameter of the body and statically sealed to the ends of the body (2), and a mechanism which may consist wholly of rigid members for intermittently expanding the entire periphery of radial sections of the element up to the whole of the inside diameter of the body in axial sequence between two ports (4) therein. A torus-like pumping chamber (3), fully sealed in all three dimensions, is thus created, which, in operation, progresses axially between the ports, transporting fluid trapped within it from one to the other.

TECHNICAL FIELD

This invention relates to peristaltic pumps and constitutes animprovement in their design and consequent performance capabilities.

BACKGROUND ART

Peristaltic pumps move fluids (liquids, suspensions and gases) by theaxially progressive radial deformation of an elastic duct or element, ofenclosed cross-section, usually in the form of annular tube, having asessential measurements a bore-size and a wall thickness.

Hitherto, the radial deformation has taken the form of a localisedcompression of the element, flattening it so that one flattened sectionof the wall is brought into fluid-tight contact with the radiallyopposite section of the wall. The compression may be effected by one ormore rollers, sliding shoes or oscillating fingers, but the operation isidentical: the sealed section is progressed a certain distance along theaxial dimension, by suitable movement or succession of the operatingmembers.

This pushes the contents ahead of the compressed section along theelement and the restitution of the elastic material behind thecompression draws in more fluid to be expelled in turn by a succeedingcompression.

This arrangement has at least four drawbacks, which limit the range ofperformance of such pumps in terms of volume, pressure and duration.

A. It is a general characteristic of elastomers which forms the elasticduct or element, that the destructive effect of rapidly and frequentlyapplied stresses and strains, necessary to the operation of aperistaltic pump, varies directly with their thickness and/or hardness.The requirement in the standard form of peristaltic pump that theelastic element should restitute from a flattened condition, against theforce of atmospheric pressure, implies that the wall of the element besubstantial in thickness or hardness and that either must increasedirectly with the bore-size of the element. Thus increasing flow-raterequirements, needing larger bores, lead inevitably to thicker and/orharder walls and shorter operating life.

B. In a standard arrangement, the regions of the wall of the element atthe radial extremes of the compression, where the walls are being foldedsharply, are subjected to very large concentrations of stresses andstrains to ensure that the seal formed by the compression is completeacross the whole width. This further promotes the breakdown of theelastomer at these particular locations.

C. As the elastic element of a standard peristaltic pump experiences thepumping pressure on its inside, increasing pressure requirementsnecessitate either yet thicker (or harder) walls, or externalreinforcements that militate against the operation.

D. A further drawback of a standard design is that the radial load onthe drive-shaft is unbalanced over at least a part of the shaft'srevolution, making heavy demands on the bearings of rotating parts andtheir supporting structures.

DE 3833833 discloses a peristaltic pump which overcomes some of theseproblems by providing an inner flexible membrane within a rigid outerbody. The mechanism for expanding the membrane uses a cam which acts anball bearings which in turn push out rings thus expanding the flexiblemembrane.

The mechanism for expanding the inner membrane is complex, requiringmany elements and detailed assembly. This creates a peristaltic pumpwhich is complicated and expensive to both assemble and repair ifnecessary.

Therefore, there is a need for a peristaltic pump that avoids or reducessome or all these problems and limitations.

DISCLOSURE OF INVENTION

Broadly, the present invention provides a peristaltic pump which employsan elastic-walled pumping element of enclosed cross-section and means ofcausing radial deformations in it progressively along its axis. It istherefore a true peristaltic pump and shares with the standard designthe advantages that the operating mechanism is isolated from the fluidbeing pumped by the wall of the element, and that it has neither glandsnor valves.

By the present invention there is provided a peristaltic pump having atubular elastic member sealed to and inside a larger sectioned morerigid outer body and an actuating means, housed within the elasticmember wherein the actuating means comprises a drive shaft and actuatingmembers and wherein the drive shaft acts through a cam arrangement onsaid actuating members for intermittently and sequentially expandingcross-sections of the elastic member against corresponding sections ofthe inside of the outer body so as to form a travelling fluid-tightseal, characterised in that the actuating members at each longitudinalposition in the axial direction, comprises a plurality of rigid elementsextending around the interior surface of the elastic member and movedradially in unison by the cam arrangement.

The elements may be substantially laminar segments of a circle the outerdiameter of which is substantially equal to that of the bore of theouter body less the wallthickness of the element.

These elements may be arranged in sets, each set being in a singleradial plane so that the sum of their major arcs form a complete circlein their expanded state.

It is preferable that the major arc length of each element of the setsubtends an angle greater than that obtained by dividing the circle bythe number of elements in an actuating member. It is also preferablethat the ends of the elements are reduced in thickness so as to allowoverlap of adjacent elements in an actuating member without substantialincrease in the total thickness of the actuating member.

A plurality of actuating members may be mounted face-to-face inside theelastic member so as to correspond in combined thickness approximatelyto the axial length of the pumping section between the inlet and outletports of the body.

The drive shaft may revolve concentrically to the actuating members andact on a chord of the elements at some stage of its revolution, but not,or less so, at another via a cam arrangement. The cam arrangement maycomprise a plurality of protrusions, each protrusion engaging a separatechord of an element of an actuating member.

The chords of the elements of the actuating members are progressivelyoffset in relation to the said drive shaft protrusions.

The cam arrangement protrusions may be rollers mounted at a suitableradial distance from the drive shaft and preferably are parallel to thedrive shaft and pump axis.

In one embodiment the elements of the actuating members may be providedwith integral protrusions on one face and mating slots in the other facecentred at an angular displacement from that of the element protrusions;dimensioned and orientated to permit the elements to move radially butnot rotationally in relation to those of neighbouring actuating members.

The two extremities of the pump outer body may be occupied by rigid,roughly cylindrical support members. These support members may also beprovided with interior faces carrying similarly dimensioned andorientated protrusions and slots to those on the elements and may engagewith those actuating members at the end of the actuating memberassembly.

This will prevent rotation at the extremities of assembly, i.e. thesupport members are held non-rotationally to the outer body and elasticmember of the pump in final assembly.

The support members may be fixedly conjoined to, or made in one piecewith, an end-cap which may locate the drive shaft and also provide themeans for sealing the end of the elastic member against the end of theouter body. Alternatively one support member may conjoin with an end-capas described but the other may be housed within the closed end of theelastic member, providing support only as no other sealing or locationis required.

In a second embodiment of the present invention the chords of theelements in each actuating member are parallel to those of otheractuating members, i.e. in line, and the cam arrangement protrusions areformed from the vertices of a polygonally cross-sectioned region of thedrive shaft, twisted to form a helix.

Accordingly, as the drive shaft rotates the protrusions of the camarrangement act on the chords of the elements of each actuating member.Each protrusion acts on a separate element. Where four elements make upan actuating member, four protrusions act on the four chords forcing theelements to move radially away from the concentrically placed driveshaft. As the elements are forced outwards, the circumference of theactuating member increases thereby expanding the elastic memberradially.

Both the first and second embodiments have the advantage that theconfiguration of the actuating members always makes a smooth continuouscurve in either the expanded state or the relax state, so that noprojections, which might damage the elastic member or any recesses,which may pinch the elastic member are formed.

The two embodiments of the present invention described above are basedon a peristaltic pump having a circular cross-section. However, alsowithin the scope of the present invention is a pump in which thecross-section of the body is non-circular and corresponding changes aremade to the outlines of the elastic member and actuating and supportmembers to maintain complete peripheral sealing against the saidcross-section of the body by an actuating member of elements in theexpanded mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying illustrative drawings in which:

FIG. 1 a schematic drawing of a peristaltic pump being within a firstembodiment of the present invention;

FIG. 2 a schematic drawing of a peristaltic pump being within a secondembodiment of the present invention;

FIG. 3 and FIG. 4 shows a transverse section of a peristaltic pump atdistinct time intervals thus showing an expanded and relaxed state inaccordance with the first embodiment of the present invention;

FIG. 3A and FIG 4 show subsequent transverse sections of a peristalticpump at a single time interval showing a helical form of the camprotrusions in accordance with the second embodiment of the presentinvention;

FIGS. 5a and 5b show an element, in plan and profile, respectively,which makes up the actuating members of the peristaltic pump accordingto the present invention;

FIG. 6 shows curve centres and slot orientation of the elements of aperistaltic pump according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The elastic member 1, which may be of any enclosed cross-section, butmay conveniently be annular, is housed concentrically within arelatively rigid member, or body 2, which has a similar, thoughinternally larger cross-section. The ends of the elastic member 1 arestatically sealed with respect to the space within the outer body 2,forming a fluid-tight region between the outer surface of the elasticmember 1 and the inner surface of the outer body 2. This region 3becomes the fluid conduit in operation.

There are two general ways in which the sealing of the ends of theelastic member may be effected. They are topologically similar, but asthey give rise to differing constructions, they are described separatelyherein as FIG. 1 and FIG. 2 where appropriate.

In FIG. 1 the wall at each end of the roughly cylindrical elastic member1 is sealed to the corresponding end of the outer body wall 2, bycompression, adhesion or fusion. The wall of the outer body 2 is piercedby at least two holes 4,40 one being near one open end of the body andthe other being near the other end. These connect the otherwise enclosedspace between elastic member 1 and outer body 2 with the outside worldand with suitable connections form the inlet 4 and outlet ports 40 ofthe pump. The axial region between these holes is designated the pumpingsection (FIG. 1).

In FIG. 2 the wall at one end of the elastic member 1 is sealed to thatof the outer body 2 as just described and that at the other end isclosed in on itself, again by adhesion, compression or fusion, butpreferably by being so moulded, so that the elastic member 1 takes onthe form commonly described as `test-tube` or `top-hat`. In this type,as shown in FIG. 2, the outer body 2 may have two port piercings 4,40,as in FIG. 1 and have its end corresponding to the enclosed end of theelastic member 1 blanked off, or it may have only one side piercing forone port and the other port formed from the other, open, end of theouter body 2. The pumping section lies between the two side ports, orbetween the side port and the closed end of the elastic member 1, asappropriate (FIG. 2).

In both FIG. 1 and FIG. 2 those sections of the elastic member 1 which,in assembly lie at either side of the pumping section, are supportedinternally by rigid, approximately cylindrical support members 5,7 of anexternal diameter similar to that of the inside of the elastic member 1in its relaxed state. These support members 5 are partially closed attheir inward ends with a face that is pierced to allow the passage of adrive-shaft 10 and attachment (FIGS. 1 and 2).

In FIG. 1 both of the above support members 5 are fixedly conjoined to,or made in one piece with, an end-cap 6 which may locate the drive-shaft10 and also provide the means for sealing the end of the elastic member1 against the end of the pump outer body 2 by wedging the exterior ofthe first against the interior of the second, or by pressing theturned-over end of the elastic member 1 against the rims of the outerbody 2, or, if the elastic member 1 is so moulded or fabricated, bycompressing a flange integral to the end of the elastic member 1 againsta mating flange formed on the end of the pump outer body 2, or anycombination of these.

In FIG. 2 one of the said support members 5, conjoins with an end-cap asabove described, but the other support member 7 is housed within theclosed end of the elastic member 1, providing support only; no othersealing or location being required. In the case of this particularsupport member 7, its outer end is closed off by a face which willconform to the shape of the closed end of the elastic member 1.

The supporters alone, or the support/end-cap 5,7 assemblies may housebearings for the drive-shaft 10, although, as will be seen, these arenot strictly necessary.

In both figures, actuating means are provided for sequentially expandingthe entire periphery of relatively thin sections of the elastic member 1against the inner surface of the outer body 2 along the said pumpingsection. These actuating means may be hydraulic or pneumatic, as in therapid inflation of annular elastic collars, or tyres, held on discs of adiameter similar to that of the element in its relaxed state. However,for simplicity of manufacture, a preferred mechanical form is nowdescribed, as it would apply to bodies and elements of annularcross-section.

In both FIG. 1 and FIG. 2 peristaltic pumps, the annular length insidethe elastic member 1 between the support members 5, and corresponding tothe pumping section of the outer body 2, is occupied by a series ofrigid elements 8. These are substantially laminar, with a profilesimilar to that of a segment of the circle whose radius is approximatelythat of the inside surface of the outer body 2, less the wall-thicknessof the elastic member 1. That is to say that one edge or arc 16 is acurve mainly of that radius and the other edge, joining the ends of thiscurve, approximates to the chord 17 of the element (FIGS. 5a-b).

A plurality of such laminar segment-like elements 8 forms a circularactuating member 11, disposed in a single radial plane normal to thepump and drive shaft axis. These actuating members are shown in FIGS. 1and 2 as hollow structures for convenience. They are however, solidstructures as shown in FIG. 5. The number of rigid elements in a set inthe actuating member 11 may be any number into which the circle of theabove described radius may be divided, although the number 2 wouldrequire a non-annular cross-section. FIGS. 3 and 4 show a four-memberset.

Each element 8 of the actuating member 11 is of an arc 16, and hencechord 17, longer than that which would exactly divide the said circle bythe number in the set and portions 18 at the ends of each element 8 arereduced in thickness so that adjacent elements may overlap to a limitedextent without increasing the overall thickness (FIG. 5b). Those partsof the curve outside the angle dividing the circle by the number ofelements 8 in the actuating member 11 may be at a different radiusand/or from a different centre to those of the main arc. These parts ofthe curve join the main arc and engage those of adjacent elements 8smoothly in the overlapped state. This eliminates projections in therelaxed state which might damage the elastic member 1. As an example, ina four-element actuating member, those parts of the curved edge outsideof 45° to each side of the perpendicular bisector may be of the sameradius C as the main arc, but at centres displaced from the centre ofthe main arc by a distance, X, to the opposite side of the perpendicularbisector and the same distance from the original centre towards theelement. `X` approximates to the radial movement of the element 8 asdescribed below (FIG. 6).

The straighter edges or chords 17 of the elements 8 are engaged byprotrusions 9 being a cam arrangement, from the drive shaft 10, passingthrough the common axis of the elastic member 1 and the pump outer body2, which act as cams as the shaft rotates. The number of protrusions 9will normally correspond with the number of elements 8 in an actuatingmember 11, and be evenly distributed around the drive shaft 10, so thatall elements 8 of the actuating member 11 are actuated in a like mannerat the same time. The action is to push the elements 8 radially outwardsto the full diameter of the segments, thus stretching and pressing theelastic member 1, in that plane, against the inner wall of the pumpouter body 2, evenly and over its entire circumference. A fluid-tightseal is thus formed at a point along the pumping section of the body,separating the annular space on one side of it from that on the other(FIGS. 3 and 4).

A plurality of such actuating members 11 occupies the length of thepumping section with only sliding play between them. At the points ofdrive shaft 10 rotation where they are not fully engaged by the camprotrusions 9, they are drawn inwards by the restitution or elasticityof the elastic member 1. As they move inwards, adjacent elements 8 willincreasingly overlap. At the inward limit of their travel, determined bythe extent of the portions 18 of reduced thickness, the elements 8 ofeach actuating member 11 lock together to a rigid structure. The extentof the overlapping thinned portions 18 is selected to lock the elements8 of the set when they are at an effective diameter substantially thesame as that of the support members 5. This ensures complete internalsupport of the elastic member 1, throughout its length, and at allstages of the pumping cycle, since the elements are supported by thesaid drive shaft 10 cam arrangement protrusions 9 at all other stages.

In order to generate a pumping action, the seal formed by one actuatingmember 11 of elements 8 in the expanded position, is progressed alongthe pumping section by sequentially expanding and relaxing adjacentactuating members 11. This is achieved by progressively skewing oroffsetting the orientation of each actuating member 11 of elements 8 inrelation to the cam protrusions 9 of the drive shaft 10.

There are two ways in which this may be effected. One is to skewsuccessive sections of the cam protrusions 9 on the drive shaft 10,whilst the orientation of the actuating members 11 of elements is keptconstant. An example of this would be, in a four-element actuatingmember design, incorporating a square-sectioned region of the driveshaft 10 corresponding to the pumping section of the outer body 2 andgiving this section a twist so that the vertices of the square (theprotrusions 9) take a helical form (as shown by FIGS. 3 and 4).

This helix will then engage and release successive actuating members 11of elements 8 at successive stages or the drive shaft's 10 revolution.

The other is to skew the orientation of each actuating member 11 ofelements 8 in relation to that of the previous actuating member 11,whilst keeping the line of the protrusions 9 parallel with the axis ofthe drive shaft 10 (as shown by FIGS. 3' and 4'). In this case, theprotrusions 9 may be in the form of cylindrical rollers, pivoted onbearings parallel to the drive shaft 10 axis and held by flange or othersuitable members 12 fixed to the drive shaft 10 at an appropriate andpreferably adjustable radial distance from it. The length of the rollersis sufficient to ensure that they engage all the elements 8 of theactuating members in the pumping section.

A variety of mechanical means which would restrain the actuating members11 from rotating about the drive shaft 10 axis, yet allow the requisitemovement normal to that axis and maintain the relative skewing of theactuating members 11 will be in accordance with this invention. Thesemay include cages with skewed peripheral slots into which the elements 8are slidingly set; rods, passing through slots in the thickness of theelements 8 which are affixed to the face of one support member 5 andtwisted before being affixed to that of the other.

The most elegant arrangement, however, in that it calls for noadditional parts, provides each element with a protrusion 13 on oneface, of a protruding length a little less than the thickness of theelement and at least one slot or groove 14 at a suitable angulardisplacement from the said protrusion 13. When assembled, theprotrusions 13 of one actuating member 11 of elements 8 engage slidinglyin the slots or grooves 14 of the adjacent actuating member 11,providing both a fixed angular displacement of one actuating member 11in relation to the next and means to allow the elements 8 of oneactuating member 11 to move in the plane normal to the drive shaft 10axis in relation to those on either side (FIGS. 5a-b). Matchingprotrusions 13 and slots 14 in the inner faces of the support memberslock the entire assembly rotationally with respect to the pump outerbody 2.

Rotation of the drive shaft 10, transmitted through the cam arrangementcarrying the said rollers or other shaft protrusions 9, bring these intoactuating contact with successive actuating members 11 of elements 8 andthus creates the required travelling wave of expansions of the elasticmember 1 against the pumping section of the pump outer body 2. Thenumber and relative alignment of the actuating members 11 of elements 8are selected to provide that the peak of one such wave is established inthe pumping section before that of a previous such peak has left it,thus ensuring continuous pumping.

More particularly, and by way of example, (FIG. 6), the elementprotrusion 13 is conveniently located on the perpendicular bisector ofthe element 8; the angular displacement of the centre of the slot, D,about the centre of the main actuator arc may be derived from theformula: ##EQU1## where W=Number of Sets in a wavelength, between peaksand S=Number of actuator segments in a set

and the orientation of the major axis of the slot or groove 14 withrespect to the perpendicular bisector of the element 8 may be at angle Min the formula: ##EQU2##

The minimum length of the slot or groove 14 may be the sum of thediameter of the said element 8 protrusion 13 and the desired radialmovement of the elements, X. This last is a function of the inverse of Sand the effective radius of the drive shaft cam protrusions 9 (orrollers) as they first engage the elements 8. It will generally beselected to be in the region of one thirtieth of the pump outer body 2bore.

Each element 8 may be provided with two or more slots or grooves 14,positioned, orientated and dimensioned to express the above formulae, orones with a similar effect, with different values of `W`, `S` and `X`.All three values are in turn dependent upon the desired relationshipbetween the flow-rate, pressure and duration capabilities for particulartypes of application, through their effect on the volume of fluiddisplaced by each expansion and relaxation cycle of an actuating member11 of elements 8.

The pump cycle, that is the travel of a complete wavelength of setexpansions, occurs S times per revolution of the drive shaft 10. Thedirection of the wave travel, and hence of the movement of the fluidbeing pumped is reversed by reversing the rotation of the drive shaft10. The pumping section may accommodate two or more wavelengths, whichmay be the same or different in the number, thickness and dimensions ofthe actuating members 11, to meet specific pumping requirements.

The drawbacks of the standard design of externally operated peristalticpump are avoided in the present design as follows:

A. The restitution of the elastic member 1 is by contraction of itsentire stretched wall. The amount of elastomer involved is directlyproportional to its diameter and hence design flow-rate of the pump, sothe strain on any given amount or circumferential length of theelastomer is substantially the same for any size without need to changethe wall-thickness.

B. In the peristaltic pump of the present invention, the stress andstrain on the elastomer are spread evenly throughout the material of theelastic member 1 at any cross-section. There are thus no localisedregions of stress and strain concentration to initiate failure.

C. The wall of the elastic member 1 experiences the pumping pressure onits outside surface and is firmly supported at all points and timesagainst this pressure by the described rigid structures 5 and 11. It isthus not the limiting factor in the pump's pressure capability.

D. As the drive shaft 10 cam protrusions 9 are always in the samerelationship with all the elements of each set of actuating members 11radially opposite each other, the radial load on the drive-shaft 10 issubstantially balanced at all points of revolution. This is why,although it is convenient to have shaft-bearings in the centre of theend-caps, these are not strictly necessary for operation and are onlylight loaded. As a consequence, the construction of this peristalticpump for a given duty will typically be lighter and more economic thanthat of previous peristaltic pumps.

I claim:
 1. A peristaltic pump comprising:a rigid outer body which istubular, said outer body having a longitudinal axis, an inlet and anoutlet; a tubular elastic member located in said outer body with aradial space provided between an inside of said outer body and saidelastic member, said elastic member being sealed to said outer body byan inlet seal and an outlet seal provided such that said inlet andoutlet of said outer body are longitudinally therebetween; an actuatingmeans housed within said elastic member for pumping a material along thespace from said inlet to said outlet, said actuating means includingadrive shaft, a series of actuating members located at a series oflongitudinal positions along said elastic member between said inlet andsaid outlet, each said actuating member including a plurality of rigidelements extending around an interior surface of said elastic member,and a cam arrangement moved by said drive shaft which intermittently andsequentially moves radially in unison said rigid elements of said seriesof actuating members such that radial cross sections of said elasticmember at each longitudinal position are intermittently and sequentiallyexpanded against corresponding sections of the inside of said outer bodyto pump the material.
 2. A peristaltic pump as claimed in claim1:wherein said outer body has a circular cross section; and wherein saidrigid elements are segments of a circle, a diameter of the circle beingabout equal to a diameter of the inside of said outer body minus a wallthickness of said elastic member.
 3. A peristaltic pump as claimed inclaim 2:wherein each said actuating member is a set of said rigidelements provided in a single plane, each said rigid element having aradially outer face formed as an arc such that all of said faces of theset form a complete circle when an associated said radial cross sectionof said elastic member is expanded against the corresponding section ofthe inside of said outer body.
 4. A peristaltic pump as claimed in claim3:wherein a major arc length of each said rigid element has an anglegreater than that obtained by dividing 360° by a number of rigidelements in each said set; and wherein each said rigid element has endsof reduced thickness which allow for an overlap with adjacent elementsof said set.
 5. A peristaltic pump as claimed in claim 1:wherein adistance between said inlet and said outlet of said outer body definesan axial length of a pumping section of said outer body; and whereinsaid series of actuating members are arranged face to face along thelongitudinal axis of said outer body with a combined thicknessapproximately equal to the axial length of the pumping section.
 6. Aperistaltic pump as claimed in claim 5, further including:an inlet rigidsupport member provided inside of said elastic member and occupying aspace between an inlet end of said series of actuating members and aninlet end of said outer body; and an outlet rigid support memberprovided inside of said elastic member and occupying a space between anoutlet end of said series of actuating members and an outlet end of saidouter body.
 7. A peristaltic pump as claimed in claim 1:wherein said camarrangement includes a plurality of protrusions.
 8. A peristaltic pumpas claimed in claim 7:wherein said drive shaft is concentricallypositioned relative to said outer body; and wherein said segments of acircle making up said rigid elements include respective chord portions,each said chord portion being engaged by a respective said protrusion toexpand the radial sections of said elastic member.
 9. A peristaltic pumpas claimed in claim 8:wherein there is a respective skewing betweensuccessive said chord portions of said actuating members of the seriesand successive protrusions of said cam arrangement.
 10. A peristalticpump as claimed in claim 9:wherein said protrusions are aligned in aseries extending parallel to said drive shaft and successive chordportions are skewed with respect to one another.
 11. A peristaltic pumpas claimed in claim 9:wherein said chord portions are parallel to oneanother and said protrusions are aligned in a helical series extendingabout said drive shaft.
 12. A peristaltic pump as claimed in claim1:wherein each said rigid element includes an integral protrusion on oneface and a mating slot in the other face centered at an angulardisplacement from said integral protrusion such that when saidprotrusion of one said rigid element is located in said mating slot ofan adjacent said rigid element said one rigid element and said adjacentrigid element can move radially with respect to one another but notrotationally.
 13. A peristaltic pump as claimed in claim 12:furtherincluding (a) an inlet rigid support member provided inside of saidelastic member and occupying a space between an inlet end of said seriesof actuating members and an inlet end of said outer body, and (b) anoutlet rigid support member provided inside of said elastic member andoccupying a space between an outlet end of said series of actuatingmembers and an outlet end of said outer body; and wherein each saidrigid support member includes an integral protrusion on one face andmating slots in the other face centered at an angular displacement fromsaid integral protrusion thereof such that when said protrusion of onesaid rigid support member is located in said mating slot of an adjacentsaid rigid element and said mating slot of the other said rigid supportmember receives said protrusion of an adjacent said rigid element,adjacent said rigid support members and said rigid elements can moveradially with respect to one another but not rotationally.